The present invention relates to an image forming device having an electrifying member in contact with an image carrier.
For an image forming device having an electrifying member in contact with an image carrier, conventionally, an occurrence of stripe-like image noise may be caused by continuous contact of the electrifying member with the image carrier for a given period of time or longer when the device is at rest. For purpose of preventing the occurrence, a number of techniques of providing a pressure-contact/separation mechanism and thereby canceling the contact between the electrifying member and the image carrier while the device is at rest have been proposed, as disclosed in Japanese Patent Laid-Open Publication No. 2002-311690, for example.
In order to resolve a problem similar to the above, as disclosed in Japanese Patent Laid-Open Publication No. HEI 8-160718, for example, techniques have been proposed in which a frequency of voltage, a peak-to-peak voltage or a current that are applied to an electrifying member is temporarily changed when the device is stopped for a given period of time.
Provision of such a pressure-contact/separation mechanism for an electrifying member as disclosed in the former publication, however, causes a problem in that the provision makes the device complicated and thereby results in cost increase. In the techniques disclosed in the latter publication, image noise that may be caused by deformation of a roller of the electrifying member associated with the pressure contact is prevented by change in various outputs until recovery from the deformation of the roller. The techniques, however, lead to occurrence of peeling discharge because intimate contact between the electrifying member and the image carrier cannot be canceled. The peeling discharge causes electrical charge to be carried partially on the image carrier, and the electrical charge results in non-uniform electrification on a surface of the image carrier and leads to image noise.